63 research outputs found
An improved global analysis of nuclear parton distribution functions including RHIC data
We present an improved leading-order global DGLAP analysis of nuclear parton
distribution functions (nPDFs), supplementing the traditionally used data from
deep inelastic lepton-nucleus scattering and Drell-Yan dilepton production in
proton-nucleus collisions, with inclusive high- hadron production data
measured at RHIC in d+Au collisions. With the help of an extended definition of
the function, we now can more efficiently exploit the constraints the
different data sets offer, for gluon shadowing in particular, and account for
the overall data normalization uncertainties during the automated
minimization. The very good simultaneous fit to the nuclear hard process data
used demonstrates the feasibility of a universal set of nPDFs, but also
limitations become visible. The high- forward-rapidity hadron data of
BRAHMS add a new crucial constraint into the analysis by offering a direct
probe for the nuclear gluon distributions -- a sector in the nPDFs which has
traditionally been very badly constrained. We obtain a strikingly stronger
gluon shadowing than what has been estimated in previous global analyses. The
obtained nPDFs are released as a parametrization called EPS08.Comment: 26 pages, 14 figures; for v2, we have revised the Table 1 and Fig.
13, and added the Fig. 14 and the Table 3 along with some more discussio
-Pb deep inelastic scattering
Nuclear-medium effects in the weak structure functions and
in the charged current neutrino and antineutrino induced deep
inelastic reactions in Pb have been studied. The calculations have been
performed in a theoretical model using relativistic nuclear spectral functions
which incorporate Fermi motion, binding and nucleon correlations.
We also consider the pion and rho meson cloud contributions calculated from a
microscopic model for meson-nucleus self-energies. Using these structure
functions, the results for the differential cross section have been obtained
and compared with the CERN Hybrid Oscillation Research apparatUS (CHORUS) data.
The results for the ratios ,
, ,
, and (i=2,3)
have also been obtained and a few have been compared with some of the
phenomenological fits.Comment: 19Pages, 12 Fig
Centrality and rapidity dependence of inclusive pion and prompt photon production in p + Pb collisions at the LHC with EPS09s nPDFs
Volume: 589The centrality dependencies of the inclusive neutral pion and prompt photon nuclear modification factors for p+Pb collisions at the LHC are studied using a spatially dependent set of nuclear PDFs, EPS09s. The calculations are performed at mid- and forward rapidities searching for an observable which would optimally probe the spatial dependence of the nuclear PDFs. In addition, we discuss to which values of the nucleus the different observables are sensitive.Peer reviewe
A global DGLAP analysis of nuclear PDFs
In this talk, we shortly report results from our recent global DGLAP analysis
of nuclear parton distributions. This is an extension of our former
EKS98-analysis improved with an automated minimization procedure and
uncertainty estimates. Although our new analysis show no significant deviation
from EKS98, a sign of a significantly stronger gluon shadowing could be seen in
the RHIC BRAHMS data.Comment: Talk given at EPS HEP 200
Exclusive production in ultraperipheral Pb+Pb collisions to NLO pQCD
We present the first NLO pQCD study of coherent exclusive
photoproduction in ultraperipheral heavy-ion collisions (UPCs) at the LHC.
Taking the generalized parton distributions (GPDs) in their forward limit, as
parton distribution functions (PDFs), we quantify the NLO contributions in the
rapidity-differential cross section, show that the real part of the amplitude
must not be neglected, study the gluon and quark contributions, chart the
scale-choice and PDF uncertainties, and compare the NLO results with LHC and
HERA data. We show that the scale dependence is significant but a scale choice
can be found with which we reproduce the 2.76 and 5.02 TeV UPC data. In
particular, we show that the process is clearly more sensitive to the nuclear
quark PDFs than thought before.Comment: 5 pages, 5 figures, contributed talk by T.L. at the XXIX
International Conference on Ultra-relativistic Nucleus-Nucleus Collisions,
Quark Matter 2022, 4-10 April, 2022, Krakow, Polan
Exclusive J/psi : photoproduction in ultraperipheral Pb plus Pb collisions at the CERN Large Hadron Collider calculated at next-to-leading order perturbative QCD
We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of J/psi mesons in heavy-ion ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider (LHC), d sigma /dy(Pb + Pb -> Pb + J/psi + Pb). For this, we account for the photon-nucleon NLO cross sections at the forward limit, the t dependence using a standard nuclear form factor, and the photon fluxes of the colliding nuclei. Approximating the generalized parton distributions with their forward-limit parton distribution functions (PDFs), we quantify the NLO contributions in the cross sections, show that the real part of the amplitude and quark-PDF contributions must not be neglected, quantify the uncertainties arising from the scale choice and PDFs, and compare our results with ALICE, CMS, and LHCb J/psi photoproduction data in Pb + Pb UPCs, exclusive J/psi photoproduction data from HERA, and LHCb data in p + p. The scale dependence in d sigma /dy(Pb + Pb & RARR; Pb + J/psi + Pb) is significant, but we can find a scale choice that reproduces the Pb + Pb UPC data at both 2.76 and 5.02 TeV collision energies. This process has traditionally been suggested to be a direct probe of nuclear gluon distributions. We show that the situation changes rather dramatically from LO to NLO: the NLO cross sections reflect the nuclear effects of both gluons and quarks in a complicated manner, where the relative signs of the LO and NLO terms in the amplitude play a significant role.Peer reviewe
The Emerging QCD Frontier: The Electron Ion Collider
The self-interactions of gluons determine all the unique features of QCD and
lead to a dominant abundance of gluons inside matter already at moderate .
Despite their dominant role, the properties of gluons remain largely
unexplored. Tantalizing hints of saturated gluon densities have been found in
+p collisions at HERA, and in d+Au and Au+Au collisions at RHIC. Saturation
physics will have a profound influence on heavy-ion collisions at the LHC. But
unveiling the collective behavior of dense assemblies of gluons under
conditions where their self-interactions dominate will require an Electron-Ion
Collider (EIC): a new facility with capabilities well beyond those In this
paper I outline the compelling physics case for +A collisions at an EIC and
discuss briefly the status of machine design concepts. of any existing
accelerator.Comment: 11 pages, 9 figures, prepared for 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 4-10 Feb. 200
Gluon Shadowing in DIS off Nuclei
Within a light-cone quantum-chromodynamics dipole formalism based on the
Green function technique, we study nuclear shadowing in deep-inelastic
scattering at small Bjorken xB < 0.01. Such a formalism incorporates naturally
color transparency and coherence length effects. Calculations of the nuclear
shadowing for the \bar{q}q Fock component of the photon are based on an exact
numerical solution of the evolution equation for the Green function, using a
realistic form of the dipole cross section and nuclear density function. Such
an exact numerical solution is unavoidable for xB > 0.0001, when a variation of
the transverse size of the \bar{q}q Fock component must be taken into account.
The eikonal approximation, used so far in most other models, can be applied
only at high energies, when xB < 0.0001 and the transverse size of the \bar{q}q
Fock component is "frozen" during propagation through the nuclear matter. At xB
< 0.01 we find quite a large contribution of gluon suppression to nuclear
shadowing, as a shadowing correction for the higher Fock states containing
gluons. Numerical results for nuclear shadowing are compared with the available
data from the E665 and NMC collaborations. Nuclear shadowing is also predicted
at very small xB corresponding to LHC kinematical range. Finally the model
predictions are compared and discussed with the results obtained from other
models.Comment: 29 pages including 7 figures; Fig.7 modified, some references and
corresponding discussion adde
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